In order to improve the efficiency of a molding system, or to enhance the qualities of the molded articles produced therein, molding systems have evolved to include a myriad varieties of post-molding molded article conditioning systems. Of these conditioning systems, most are configured to simply alleviate in-mold cooling time, and hence operate to reduce the overall duration of the molding cycle. However, it is also known to configure and use post-molding molded article conditioning systems to enhance the characteristics of the molded article (e.g. impart localized crystallinity in the plastic structure; impart a temperature profile to the molded article that is suitable for a subsequent molding process; reshaping of a portion of the molded article; removing of unwanted features such as gate vestige; etc.).
As an example, and without specific limitation, a typical injection molding system 2 that includes a post-molding molded article conditioning system is shown with reference to FIG. 1. The injection molding system 2 is configured for the production of plastic preforms 32 (or parisons) that are used in the blow molding of bottles. As a further example, the injection molding system could be an INDEX (Trademark of Husky Injection Molding Systems Ltd.) molding system such as that described in U.S. Pat. No. 6,113,834 to Kozai et al., issued Sep. 5, 2000.
Referring back to FIG. 1, the injection-molding system 2 comprises molding structure that includes, without specific limitation, a clamp unit 4 with an injection mold arranged therein, an injection unit 6, and a robot 8 with an end-of-arm-tool (EOAT) 11 arranged thereon. The injection mold comprises complementary mold halves 12, 14, with one or more preform mold cavities configured therein. Each mold cavity is configured in a stack of cooperating molding inserts that include a core 22 and a cavity 24, that are disposed on the mold halves 12, 14. The injection mold halves 12, 14, (shown in an open configuration in FIG. 1) are mounted between a fixed and a movable platen 16, 18 of the clamp 4. A set of tie bars 20 connect the platens 16, 18 with a clamp mechanism 21. The EOAT 11 comprises a take-out plate 28 with a one or more preform cooling tube assemblies 30 arranged on a surface thereof. The number of cooling tube assemblies 30 on the surface of the take-out plate 28 is equal to, or a multiple of, the number of mold cavities configured in the mold.
The EOAT 11 may be advantageously configured to include the cooling tube assembly 30 that is described in commonly assigned U.S. Pat. No. 6,737,007 to Neter et al., issued May 18, 2004, or the similarly configured cooling tube assembly described in commonly assigned PCT patent application WO 03/086,728 to Pesavento, published Oct. 23, 2003. In particular, the cooling tube assembly 30 is configured for a post-molding conditioning of at least a portion of a malleable injection molded perform received therein. The cooling tube assembly 30 includes a conditioning body (not shown) with a conditioning cavity that is configured therein along a cooled inner conditioning surface. The conditioning cavity is configured to sealingly receive, and thereafter condition, the portion of the preform by expanding at least a portion of an outer surface thereof into contact with the cooled inner conditioning surface. Accordingly, the conditioning body is configured for connection with a heat dissipation path (not shown) and an air pressure structure, via the take-out plate 28, to perform the preform conditioning as will be explained in further detail hereinafter. The air pressure structure may be selectably configured to be connected to a vacuum pump 34 or a source of compressed air (not shown). In more detail, the conditioning body is configured to include a porous insert (not shown) that is formed from a thermally conductive porous material, such as porous aluminum. The porous insert is configured to include a porous inner conditioning surface configured therein that provides at least a portion of the inner conditioning surface of the conditioning cavity. The porous insert is further configured to connect the inner porous surface thereon with the heat dissipation path and the air pressure structure to perform the conditioning of the preform portion.
An injection molding process cycle for the production of one or more preforms begins with the step of closing of the mold by moving of the movable platen 18 relative to the fixed platen 16 by means of stroke cylinders (not shown), or the like, to close the mold. A mold clamping force is then applied to the mold halves 12, 14 by the clamp mechanism 21. Next, the injection unit fills and pressurizes the mold cavities and a corresponding number of preforms are formed. The mold is then opened once the molded preforms have been partially cooled in the mold to an extent required to avoid significant deformation thereof during a subsequent step of ejection. The robot 8 then positions the end-of-arm-tool (EOAT) 11 between the mold halves 12, 14 to align the cooling tube assemblies 30 with the one or more preforms that are retained on their cores 22. The preforms are then ejected from the mold cores 22, by an actuation of a mold stripper plate 33, and the preforms are transferred into the cooling tube assemblies 30. The robot 8 then withdraws the EOAT 11 from between the mold halves 12, 14 and the molding cycle can repeat.
Contemporaneously to the molding of a subsequent shot of preforms 32, a post-molding conditioning process is performed in the cooling tube assemblies 30 that begins with the step of transferring the partially cooled, and hence malleable, preforms 32 from the mold cores 22 into the cooling tube assemblies 30. The foregoing transfer is generally assisted by a suction flow of air that is established along the inner conditioning surface of the conditioning cavity to a suction channel (not shown) that is configured in an end portion in the conditioning body and that is connected with the air pressure structure. Once at least a portion of the preforms 32 are sealingly received in the cooling tube assemblies 30, an outer surface of the each preform portion is expanded into contact with the cooled inner conditioning surface of the respective conditioning cavity. The foregoing is accomplished by evacuating any air contained between the outer surface of the preform 32 and the inner conditioning surface of the conditioning body through the porous inner conditioning surface of the porous insert under an applied vacuum provided by the air pressure structure/vacuum pump 34. Thereafter, the outer surface of the preform 32 is kept in contact with the cooled inner conditioning surface of the conditioning body, by maintaining the vacuum, until the preform 32 has been solidified to an extent required to maintain its shape once ejected from the cooling tube assembly. Thereafter, the preforms 32 are ejected from their respective cooling tube assemblies 30 by connecting the air pressure structure to the source of compressed air and pressurizing of the conditioning cavity by blowing air through the porous inner conditioning surface of the porous insert and also possibly through the pressure channel.
It is the ability of the cooling tube assembly 30 to expand, and to maintain, any desired portion of the outer surface of a preform 32 in an intimate contact with the cooled inner conditioning surface thereof that provides for significant advantage. In particular, the intimate contact provides for optimal conductive heat transfer efficiency therebetween, while also assuring a homogenous cooling of the outer surface of the preform that avoids certain types of defects (e.g. banana shaped preforms, ovality, gate vestige stretching, gate vestige crystallinity, etc.). Moreover, it is also possible to configure the cooled inner conditioning surface of the cooling tube assembly 30 to perform a shape correction of the preform (i.e. substantially prevent preform shape variations that are commonly caused by variations in the molding process, post-molding cooling, shrinkage, etc.) or to significantly re-shape the preform as desired (e.g. for the purposes of preferential blow molding as described in detail in WO 03/086,728, as introduced hereinbefore.
Despite the significant improvements that are available through the use of the various known molded article conditioning apparatus, and in particular the cooling tube assembly 30 described hereinbefore, there does however remain areas for further improving the structure and operation thereof.
For instance, while it is desirable to provide the cooling tube assembly 30 with a suction channel, as previously described, for assisting in the transfer of the preform 32 from the mold core 22 thereto, a continued application of vacuum pressure therethrough during the step of preform expansion and cooling can be the cause certain defects in the preform 32. In particular, a gate vestige 80A located on an end portion 80 of the preform 32, as shown with reference to FIG. 3B, can be significantly deformed as it is being sucked down the suction channel. Accordingly, it is desired to configure an improved cooling tube assembly that includes a means for controlling the suction flow through the suction channel whereby the suction channel remains connected to the air pressure structure only during the step of preform transfer.
Similarly, it is desired to configure the porous insert with an improved structure for connecting the air pressure structure with the inner porous surface disposed thereon.
Likewise, it is desired to configure a porous insert with a simplified cooling configuration.